The present invention relates to piston-type flush valves or flushometers and more specifically to an improved seal for the piston assembly. The piston assembly reciprocates during operation of the flush valve and the lip seal creates a dynamic barrier between the pressure chamber above the piston assembly and the discharge outlet below it. The piston seal of the present invention is advantageous in that it requires less stringent assembly criteria, provides a seal which has a substantially extended life, and improves flush volume consistency.
The lip seal in the present invention functions as a bearing to keep the piston assembly sliding along its axis, straight in the bore of the flush valve. The particular seal design reduces the effect of retaining screw torque on the lip geometry. The lip seal comprises an insert and an elastomer molded over the insert. The insert functions to stiffen the seal itself. The injection molded assembly of the insert and the elastomer has a plurality of raised bosses that carry the load applied by the screws that hold the piston assembly together. The presence of such bosses transfers the load between the mating parts of the piston assembly and prevents excessive deformation of the lip seal geometry.
In lip seals currently used in this environment, if there is distortion, which may result from over application of torque to the screws that hold the piston assembly together, the piston will not cycle properly with an extreme result being the piston lodging in the bore of the flush valve. Further, the applied screw torque required for proper assembly of the piston components causes the upper edge of the seal to expand outwards, decreasing the clearance between the lip seal and the bore of the flush valve body. One result can be that the piston can wedge in the bore. Another result is that over time the seal itself will wear, resulting in a change in the friction between the seal and the bore of the flush valve which results in less consistency in the flush volume when the valve is operated.
The present invention provides an insert in which there are flexible fingers incorporated into the perimeter of the lip seal which center the lip seal, reinforce the elastomer of the lip seal, and maintain a uniform pre-load applied by the lip seal to the wall of the chamber within which the piston assembly moves. The fingers of the insert have a helical twist which extends the effective length of the fingers which consequently reduces the stress on the insert itself. This design also allows the fingers to overlap which distributes the compressive load more uniformly through the seal.
The present invention relates to piston-type flushometers and more specifically to an improved lip seal for use in such an environment.
A primary purpose of the invention is to provide a lip seal which has less stringent assembly criteria, provides improved flush volume consistency and a piston assembly with a substantially increased effective life.
Another purpose is a piston assembly lip seal as described which has an insert which carries and distributes the torque load from the screws that attach the lip seal to the piston assembly.
Another purpose of the invention is to provide a lip seal which has reinforcing fingers extending outwardly toward the body of the flush valve which function to center the seal, reinforce the elastomer at the lip seal, and maintain a uniform pre-load by the seal against the bore of the flush valve within which it moves.
Another purpose is a lip seal for the use described which maintains consistency in valve operation over the life of the valve.
Other purposes will appear in the ensuing specification, drawings and claims.